The Fukushima Daiichi (No. 1) nuclear plant, where an explosion was reported Saturday, has lost its emergency cooling system at another reactor, Japan's nuclear power safety agency said Sunday, according to Reuters.

The emergency cooling system is no longer functioning at the No.3 reactor. The facility must urgently secure a means to supply water to the reactor, an official of the Japan Nuclear and Industrial Safety Agency told a news conference.

Japanese officials earlier told the International Atomic Energy Agency that they have begun filling the nuclear reactor container with seawater to cool the reactor, Reuters reports. However, it could take 10 days to fill the container, and salt and impurities in the seawater might prevent the reactor from functioning in the future.

Officials confirmed earlier that the explosion at the Fukushima No. 1 nuclear plant did not occur in its reactor, and they insist that the situation will not develop into a catastrophe, Kyodo reports. Chief Cabinet Secretary Yukio Edano said at a hastily convened news conference that the operator of the plant, Tokyo Electric Power Co., has confirmed there is no damage to the steel container that houses the reactor.

Pressure in the reactor is at 1.5 times the normal level, according to Japan's nuclear safety agency. Slightly radioactive vapor needs to be released to reduce the pressure.

JAPAN: 6:30 a.m. (JST) / 4:30 p.m. (ET), Saturday

Deciphering the Fukushima reactor event's danger rating

On the International Nuclear and Radiological Event Scale, from one to seven, the damage to the Fukushima nuclear plant has been rated a four by Japan's nuclear safety agency. By comparison, the 1986 Chernobyl disaster was a seven, and the 1979 Three Mile Island meltdown was a five.

For anyone confused by how an evolving disaster of mass proportions can be distilled into a numerical rating, Reuters has a breakdown of the International Atomic Energy Agency's explanation of the rating system. A rating of four, according to the IAEA, refers to an "accident with local consequences":

A minor release of radioactive material unlikely to result in implementation of planned countermeasures other than local food controls and fuel melt or damage to fuel resulting in more than 0.1 percent release of core inventory and the release of significant quantities of radioactive material within an installation with a high probability of significant public exposure.

Other nuclear incidents with a rating of four occurred in Tokaimura, Japan, in 1999, Saint Laurent des Eaux, France, in 1980, and Fleurus, Belgium, in 2006.

JAPAN: 6:27 a.m. (JST) / 4:27 p.m. (ET), Saturday

140,000 people near power plants have been evacuated

Caretakers carry a woman who is evacuated from a nursing home, which is located in the evacuation area near the Fukushima Daini nuclear plant, at a temporary shelter in Koriyama March 13, 2011. (REUTERS/Kim Kyung-Hoon)

IAEA says they were told by Japan that so far 140,000 people near two nuclear plants have been evacuated, Reuters reported.

JAPAN: 6:16 a.m. (JST) / 4:16 p.m. (ET), Saturday

160 could have been exposed to radiation

Japan nuclear safety agency says the number of people possibly exposed to radiation from Fukushima plant could reach 160, Reuters reported. Nine people have shown signs of possible exposure.

Tsunami waves that hit the West Coast of the United States on Friday smashed ships, ripped out docks and caused flooding in Hawaii, CNBC reported. The cleanup may cost millions

At least five people along the West Coast were swept out to sea Friday, according to the San Jose Mercury News. Four of those people have been rescued, but the fifth person was missing and presumed dead.

Six-foot waves crashed into a harbor in Crescent City, Calif., America's "tsunami capital", which has been hit by 31 tsunamis before this one. The sea level rose nearly three feet as far south as San Diego on Friday. The waters destroyed the busiest recreation port on the Oregon coast.

A tsunami advisory was in effect for much of the West Coast on Saturday morning but has since been canceled.

"I've never seen anything like this," residents said of the damage. WATCH:

PERU: 3:15 p.m. (PET) / 3:15 p.m. (ET), Saturday

Peru feels effects of tsunami

Members of Civil Defence, stand guard at the port of El Callao in Lima on March 11, 2011, after Peru launched a tsunami warning. (ERNESTO BENAVIDES/AFP/Getty Images)

Civil defense officials in Peru had ordered the evacuation of Pisco and Paracas, two towns south of Lima that had suffered the effects of tsunamis in past years.

The rest of Latin America's Pacific nations reported little or no damage.

JAPAN: 5:10 a.m. (JST) / 3:10 p.m. (ET), Saturday

Nuclear plant worker dies from injuries

The Post's Chico Harlan reports from Tokyo that a worker at the Fukushima Daiichi Unit 1 nuclear plant has died from his injuries after becoming trapped in the exhaust stack of the plant, according to the World Nuclear Association. The plant's cooling system failed yesterday, and pressure built up to a dangerous level, necessitating the release of radioactive vapor. Four other workers were reportedly injured in the explosion and have been hospitalized.

The United Nations says the risk from Japan's radiation leak appears to be "probably quite low," al-Jazeera reported.

The World Health Organization's Gregory Hartl said: "At this moment it appears to be the case that the public health risk is probably quite low. We understand radiation that has escaped from the plant is very small in amount."

The French Nuclear Safety Authority said any radioactive pollution from the explosion at the Fukushima power plant will probably be blown out over the Pacific Ocean, thanks to favorable winds.

Radiation from the crippled nuclear power plants in Japan poses a host of potential health risks that range from "possibly severe toxic effects in workers exposed to high doses to long-term increased rates of many cancers," Rob Stein reported. Read more here.

JAPAN: 4:43 a.m. (JST) / 2:43 p.m. (ET), Saturday

Japan to distribute potassium iodide pills

Japanese officials have said they are planning to distribute potassium iodide pills to people in affected areas to prevent thyroid cancer from radiation exposure.

Back in 2005, when the Bush administration was struggling to distribute these pills to people living within 20 miles of nuclear plants, as mandated by Congress, USA Today explained how these pills work:

A nuclear accident produces radioactive iodine. Potassium iodide pills, if taken quickly, fill the thyroid with non-radioactive iodine, thereby blocking the radioactive element from the thyroid. Thyroid cancer would be a leading health concern... in the event of a radioactive iodine leak.

The prefectural government of Fukushima doubled the evacuation area around Fukushima No. 1 power station from an earlier established 10-kilometer (6.3-mile) radius to a 20-kilometer radius, Japanese television station NHK World reported earlier Saturday. The decision was made at a nuclear disaster task force meeting.

The prefectural government is working to determine which towns and villages fall under the new evacuation order.

The evacuation area for the No. 2 station will remain at a 10-kilometer radius.

JAPAN: 3:00 a.m. (JST) / 1:00 p.m. (ET), Saturday

Tsunami felt on West Coast

The tsunami that ravaged Japan was also felt on the West Coast Friday. It ripped docks out and damaged or destroyed a number of boats in California's Santa Cruz Harbor. WATCH:

JAPAN: 2:40 a.m. (JST) / 12:40 p.m. (ET), Saturday

Three Japanese residents exposed to radiation

At least three Japanese residents of a town near the nuclear plant hit by an explosion were exposed to radiation, Japanese television station NHK reported Saturday.

The announcement by the Fukushima Prefecture was made amid fears of a major radioactive leak at the plant.

The three residents were part of a group of some 90 patients hospitalized in the town of Futaba-machi. The residents were chosen at random by doctors for tests linked to the nuclear incident.

JAPAN: 2:31 a.m. (JST) / 12:31 p.m. (ET), Saturday

Death toll could top 1,700

The death toll has already surpassed 600 and could top 1,700, Kyodo News Service reported Saturday.

Several cities and towns have been virtually destroyed, Kyodo said.

JAPAN: 2:20 a.m. (JST) / 12:20 p.m. (ET), Saturday

Children tested for radiation

After the explosion and radiation leakage at Tokyo Electric Power Co's Fukushima Daiichi nuclear power plant, children in the area are being tested for signs of radiation.

Edwin Lyman, a senior scientist with the Union of Concerned Scientists, said Japan must work to protect children against exposure to radioactive iodine, ABC reported.

The chief cabinet secretary, Yukio Edano, said that radiation around the plant had, in fact, started to decrease.

Officials in protective gear check for signs of radiation on children who are from the evacuation area near the Fukushima Daini nuclear plant in Koriyama, March 13, 2011. (REUTERS/Kim Kyung-Hoon)

JAPAN: 2:07 a.m. (JST) / 12:07 p.m. (ET), Saturday

Could Japan's damaged nuclear power plants turn into another Chernobyl?

Japan officials said earlier Saturday that nuclear meltdowns were possible at the damaged Fukushima nuclear power plants. But how serious could the meltdown get? Could this become another Chernobyl? The Post's energy reporter Steven Mufson weighs the possibilities in this audio report from Washington:

Fishing boats rest piled up on debris in the northern Japanese city of Kesennuma in Miyagi prefecture on March 12, 2011. (YOMIURI SHIMBUN/AFP/Getty Images)

Local fire company members search through a home collapsed by Friday's powerful earthquake-triggered tsunami during a search operation at Yamamoto town, Miyagi prefecture, Saturday, March 12, 2011. (AP Photo/Kyodo News)

Japan's hospitals were stretched to breaking point Saturday, helping not just patients but also people who had lost their homes and needed a place to stay, the Japan Times reported.

Due to power outages, hospitals said they had limited electricity and also voiced fears that water might run out quickly.

A hospital in Sendai was treating 400 patients while providing shelter to dozens of local residents. Some spent the night in hallways.

The hospital's in-house generators were capable of maintaining power for just two days, so officials worried they might not be able to use artificial respirators.

"The situation concerns the lives of our patients. We really need more power and other supplies," hospital official Yutaka Hoshi said.

JAPAN: 1:08 a.m. (JST) / 11:08 a.m. (ET), Saturday

For those concerned about specific U.S. citizens in Japan, the State Department has set up this email address: japanemergencyusc@state.gov

JAPAN: 12:30 a.m. (JST) / 10:30 a.m. (ET), Saturday

First wave of U.S. aid arrives

The first wave of promised aid from the United States began arriving in Japan on Saturday, CNN reported. More aid, including equipment, staffers and search-and-rescue teams, is expected to arrive Sunday.

Helicopters from the U.S. naval air facility at Atsugi, Japan, delivered 1,500 pounds of rice and bread to Shiroishi, a town near the area hardest hit by the quake.

Two U.S. destroyers are preparing to assist with at-sea search and rescue and recovery operations. A third destroyer and other U.S. ships are on the way.

The 3rd Marine Expeditionary Force will also provide humanitarian assistance in an operation called Operation Tomodachi, or "friendship."

The U.S. Navy has released video of HH-60 Sea Hawk helicopters loading supplies for the humanitarian relief effort in Japan. WATCH:

Roughly 9,500 in Minamisanriku -- a town of 17,000 in Miyagi Prefecture -- remain missing or unaccounted for, according to the Kyodo news agency, citing local government officials. As of Saturday evening, police said that 621 were confirmed dead, with thousands more missing. More than 210,000 had been evacuated.

JAPAN: 11:25 p.m. (JST) / 9:25 a.m. (ET), Saturday

Washington Post reporter Chico Harlan is on the ground in Japan and live-tweeting.

Here's what other people are saying right now on Twitter:

JAPAN: 11:25 p.m. (JST) / 9:25 a.m. (ET), Saturday

Are you in Japan right now? Did you experience the earthquake or the tsunami? What did you witness? How were you affected?

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